Unionization is the process of joining or forming a labor union (aka trade union), which is an organization of employees who work together to negotiate better conditions for themselves, like higher pay.
Unionizing is a long and public process. If your store is involved, you would probably know about it already, but at the very least you would be given a chance to vote yes or no on joining a union.
$1$1A video from Bloomberg News about unionization at Starbucks:
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